Determination of the valence-band offset in AlGaAs Type II heterostructures.

Photoluminescence spectra from Al(0.37)Ga(0.63)As/AlAs multiple- quantum-well structures are presented which provide the first direct optical measure of the valence-band offset at a semiconductor heterojunction. The experiment takes advantage of the crossover occurring at a critical aluminum concentration above which the indirect X minimum in the AlAs becomes the lowest-energy conduction band in the system, and recombination occurs across the interface. The resulting sub-bandgap emission allows a direct determination of the valence-band offset.